A positive-electrode active material powder is used for nonaqueous secondary battery such as a lithium secondary battery. The nonaqueous secondary battery is practically used for a power source for cellular phones and laptop computers, and the attempts are made to apply the nonaqueous secondary battery for applications of middle size and large size such as automobiles and electric power storage units.
Japanese Unexamined Patent Publication No. 2002-158011 discloses, as a conventional positive-electrode active material powder, a positive-electrode active material powder containing a core including a lithium compound constituting secondary particles having an average particle diameter of from 1 μm or more and less than 10 μm, and a surface treated layer containing a compound such as an oxide containing a coating element formed on the core.